1. Field of the Invention
The invention relates to a magnetic-tape cassette comprising a housing formed with a magnetic-head opening, a magnetic tape arranged in the housing, a part of said tape extending across the magnetic-head opening, and a resilient element provided with tape guides, which element, viewed from the exterior of the housing, is situated behind the magnetic tape at the location of the magnetic-head opening, which magnetic-tape cassette is suitable for cooperation with a magnetic-tape apparatus comprising tape-transport means for transport of the magnetic tape in a longitudinal direction, magnetic-head means having a head face for cooperation with the magnetic tape in an operational situation, and further tape guides which, viewed in the direction of tape transport, are situated upstream and downstream of the magnetic-head means.
2. Description of Related Art
A magnetic-tape cassette of the type referred to above is known from U.S. Pat. No. 4,564,157. The tape guides keep the magnetic tape in a specific position in such a way that the magnetic tape does not come into contact with parts of a magnetic tape apparatus when the cassette is loaded into this apparatus. However, in the operational position the tape guides are pressed away by further tape guides of the apparatus and the tape guides are not in contact with the magnetic tape.
This prior-art cassette does not provide an improved contact between the magnetic tape and the magnetic head as in the previously proposed improvements to the well-known Compact Cassette system, which comprises cassettes as standardised in IEC publication 94 and apparatuses comprising additional tape guides for improved tape guidance, as known from European Patent Specification 0,063,398. The apparatus known from said Patent Specification comprises a magnetic-head unit having two tape guides at opposite sides of the magnetic head, which tape guides comprise a height limiter and a control element for maintaining a tape edge constantly in contact with the height limiter. In magnetic recording it is essential that during reading of signals from a magnetic tape the transducing gap of the magnetic head is inclined at the same angle (azimuth angle) relative to the magnetic tape as during recording of said signal. If these two azimuth angles differ azimuth errors arise during reading, resulting in loss of signal. The height limiters of the known apparatus ensure that the magnetic tape always occupies the same position relative to the magnetic head. For this purpose the edge of the magnetic tape should be constantly in contact with the height limiters, which is achieved by means of the control elements. These elements comprise inclined tape guide faces which press against the other edge of the magnetic tape. In order to prevent the magnetic tape from being curled or folded the tape should be wrapped around the cylindrical guide surfaces of the tape guides at a specific minimum angle. The cylindrical shape leads to an increased stiffness of the magnetic tape which reduces the likelihood of the curling or folding. Said minimum angle may not be obtained as a result of tolerances in the manufacture of the apparatus, so that the height limiters have no effect.
The prior-art construction results in the wrapping angle of the magnetic tape around the magnetic head being smaller than the wrapping angle in the absence of said tape guides. As a result of this, the tape-to-head contact becomes more critical in relation to the signal transmission and, in particular in the case of high-frequency signals, such as for example digital signals, this may give rise to transmission errors.
In a rapid-search mode of the apparatus, in which the magnetic tape is moved past the magnetic head at increased speed and in which the magnetic head occupies a partly withdrawn position, the wrapping angle of the magnetic tape around the tape guide becomes even smaller. A smaller wrapping angle leads to having an increased curling tendency of the magnetic tape, so that the height limiter fails to limit the position of the magnetic tape and azimuth errors are more likely to occur. Since in the operational position the tape guides of the prior-art cassette are not in contact with the magnetic tape this cannot lead to an improved tape-head contact.